True morphology of the Azotobacteraceae—filterable bacteria

Abstract

The history of bacteriology up to the 1950s contains many references to filterable forms of bacteria but misconceptions regarding the nature of filterability eventually made the entire phenomenon an unresolvable paradox^1–4. Although the existence of filterable azotobacter has often been reported^5–9, so much doubt in these results has been expressed^10,11 that now Bergey¹² does not even mention filterability. In 1965 we reported the resistance of soil azotobacter to γ rays and concluded that the possibility of a very small Azotobacter form could not be dismissed¹³ and as a result of studies on survival in soil, we suggested the possible existence in soil of a still undiscovered phase of the Azotobacter cyst¹⁴. We report here the discovery of these small, soil azotobacter and provide evidence to support this claim.